Storm warning method and apparatus

ABSTRACT

An apparatus and method of detecting, tracking and displaying lightning activity is disclosed. A lightning stroke has associated therewith electric and magnetic field components characterized by maximum rise times and minimum power levels. The field signals comprise a plurality of sub pulses also. An electric field antenna and a pair of magnetic field antennas are disposed to receive the field components associated with lightning activity. Control circuitry cooperating with rise time and threshold measuring which operates on the field signals received by the antennas generates control signals including integration and sampling control signals for integrating the electric and magnetic field signals over a predetermined time interval (preferable one hundred microseconds) and for sampling and holding the field signals at each of the sub pulse peaks. Preprocessing circuitry upon command from a programmable microprocessor A to D converts the integrated and sampled field components where they are stored as digital data in FIFO memories. In response to control signals from the control circuitry the microprocessor transfers the digital data from the FIFO memories to its own memory whereupon it determines the azimuth and elevation angles to the lightning activity based on the sampled field data and determines the range based on the ratio of the magnetic to electric field components using the integrated values of the magnetic and electric fields. The angle and range information is transmitted to a display processor and display where it can be displayed in a variety of formats. Where the apparatus is mounted in an aircraft, the speed of the aircraft and changes in heading are factors into the determination and display of the angles and range.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus and method for displaying regionsof lightning activity.

Thunder storms characterized by turbulence and electrical activity(lightning) create great dangers particularly to air travel. It istherefore desirable to locate thunder storm activity as accurately aspossible so that thunder storms can be tracked, predicted and avoided.Lightning associated with the mature stages of thunder storms generateselectrical signals that propagate through the atmosphere. The detection,recognition, accurate measurement and analysis of these electricalsignals provide a basis for storm tracking, avoidance, etc.

Lightning flashes are composed of a series of high current lightningstrokes, each stroke being preceeded by a lower current discharge calleda leader. The duration of electrical activity associated with alightning stroke varies but in many instances last as much as a hundredmicroseconds. The initial rise time of electrical signals associatedwith a lightning stroke almost never exceeds five microseconds.Following the first peak of the electrical signals of a lightningstroke, lesser signals of sub-microsecond duration but with fast risetimes (of five microseconds or less) will occur.

U.S. Pat. No. 4,023,408 discloses a storm mapping system which detectselectrical activity caused by weather phenomenon such as lightningstrokes. The system is intended to operate on the far field (orradiation field) pattern generated by the lightning stroke. According tothe disclosure, the far field pattern is characterized mainly by a lowfrequency spectrum with maximum amplitude signals occurring betweenseven and seventy three kilohertz (KHZ). A trio of antenna sensors, anelectric field antenna and two crossed magnetic field antennas, are usedand each is connected to a tuned receiver on a center frequency of fiftyKHz. The crossed loop magnetic field antennas are used to locate thelightning signals in azimuth angle by comparing the relative magnitudeof the signals induced in the cross loop sensors to the electric fieldantenna in a conventional manner. The magnetic field signals are timecorrelated with the electric field signals before integration. Thisprovides some measure of avoiding unwanted noise like signals.Integration of the correlated signals is formed for 0.5 milliseconds butonly after the vector sum of the magnetic field sensor signals is foundto exceed a predetermined threshold value. The algebraic sum of themagnetic field sensor signals is amplified and then squared. This signalis used to divide the integrator output signals thereby reducing themagnitude of larger correlated integrated signals below the magnitude ofsmaller ones. These inverted signals then drive a display such as a CRTdisplay to show larger signals closer to the observation point andsmaller signals farther away.

This system has been used on aircraft and appears to work well, but itdepends heavily on the magnitude of correlated electric and magneticfield signals to provide a measure of the range of the signal from theobservation point of the equipment. Accordingly, the accuracy of rangeestimates may be affected by the variation in the severity of thethunder storms. Also, some of the detailed characteristics of lightningstroke signals are not utilized to discriminate between interferingsignals and true lightning electrical signals.

The Ruhnke U.S. Pat. No. 3,715,660, discloses an apparatus fordetermining the distance to lightning strokes. It does not measure orcalculate the direction of the storm. Like U.S. Pat. No. 4,023,408 itdiscloses the use of crossed magnetic field sensors and an electricfield sensor. Discrimination of lightning signals over background andinterfering signals is provided by filtering the output of the antennaelements at one kilohertz. The square root of the outputs of themagnetic field sensors are compared with the absolute value of theelectric field element to produce a number which is related to the ratioof the magnetic to electric fields. This ratio is related to rangeaccording to FIG. 8 of the subject application. The inventor, Ruhnke,first described this curve in a NOAA Technical Report ERL 195-APCL 16.

As disclosed in the Ruhnke patent, range is calculated based on the|H/E| ratio curve of FIG. 8 of the subject application. However, thecurve shows that ambiguities in range occur for some |H/E| values since|H/E| decreases after peaking at about 50 Km. No mention is made of howto resolve the ambiguity. Similarly, the sole discriminate forbackground noise relies on a one kilohertz filter. The full informationcontained in the details characterizing lightning strokes are notutilized.

Within a few years of Doctor Ruhnke's effort, Doctor E. Krider andassociates built a magnitude direction finder utilizing the initial fewmicroseconds of a lightning stroke which provided accurate directions tothe channel basis lightning discharges. Tests on a number of storms atdistances of ten to one hundred kilometers indicated angular resolutionin the range of one to two degrees. Another important observation by Dr.Krider was that the first few microseconds of a wide band magneticwaveform are due to the radiation field term and the general fieldequation and that the lightning channel near the ground tends to bestraight and vertical which minimizes polarization errors. Dr. Krider'sinstrument did not actively address ranging.

SUMMARY OF THE INVENTION

The present invention comprises an apparatus and method for displayingthe location of regions of recently occurring lightning activity. Theinvention comprises a receiving means for separately receiving theelectric (E) and magnetic (H) field components of lightning signals overa wide range of frequencies. In the preferred embodiment, the receivingmeans includes a pair of cross-loop sensors and an electric fieldsensor. These sensors measure the time rate of change of the magneticand electric flux densities. The outputs are suitably amplified andintegrated to provide a measure of the E and H fields of the lightningsignals.

Recognition circuitry means connected to the receiving means recognizeslightning signals received by the receiving means and discriminatesagainst interfering signals and background noise. The recognitioncircuitry means, in the preferred embodiment, comprises rise timecircuitry means and threshold circuitry means which responds to the risetime of the electric field signals and the amplitude of the magneticfield components respectively. Alternatively, the rise time of themagnetic field components can be utilized. When a positive rise timesignal and a positive threshold signal is present at the same time,first gating circuitry is triggered which provides a signal indicatingthat a bonafide lightning strike has occurred. In the preferredembodiment, only rise times of less than five microseconds will providea positive signal.

Control circuitry means connected to the recognition circuitry meansprovides control signals to the apparatus. It provides integrationcontrol signals, sampling control signals, and an interrupt signal.

Integration circuitry means connected to the receiving means and to thecontrol circuitry means, separately integrates the total E field and Hfield received from the receiving means. The integration is performedover a predetermined time interval in response to integration controlsignals received from the control circuitry means. In the preferredembodiment, when the rise time and theshold of the received lightningsignals indicate that a valid lightning stroke is present at the E and Hfield sensors, switching circuitry is activated in response to theintegration control signals to allow the output of the receiving meansto be integrated over the predetermined time interval. In the preferredembodiment, this predetermined time interval is one hundredmicroseconds.

The output of the receiving means is also transmitted to the samplingmeans which in response to sampling control signals from the controlcircuitry means samples the E and H field values of the receiving means.These samples are provided each time the electric field value peaksafter a rise time which is less than the predetermined rise time, inthis case five microseconds. These fast rise time signals are held atthe peak value by track and hold circuitry and then converted by A to Dconverters and stored in a first-in first-out (F IF O) memory.

When the predetermined integration interval is over, that is, when thelightning stroke activity ends, an interrupt signal from the controlcircuitry means is transmitted to a programmable processing means whichin turn reads the contents of the F IF O memory into its own read onlymemory (ROM). At the same time, the processing circuitry means alsoreads the integrated E and H field values for the predetermined intervalthrough a multiplexer circuit and one of the F IF O memories. Thesampled E and H field values read from the F IF O's are related by thefollowing equation:

    -H.sub.x sin (φ)+H.sub.y cos (φ)=E.sub.z /(Z.sub.o sin (θ))

where φ is the azimuth angle to the lightning stroke and θ is theelevation angle. Two sample sets of the E and H field values entered inthe above equation results in the simultaneous solution of two equationsto solve for θ and φ. Because in general each lightning stroke producesa plurality of sampled E and H field values, at least one set of valuesfor θ and φ can be solved for by the processing circuitry means.

The total magnetic field value is calculated from the sampled magneticfields and the value compared with a predetermined field strengths toestimate which of several range regions the lightning stroke occurredin, that is, in the near, mid, or distant range region. Similarly, theintegrated H field value is also compared to predetermined fieldstrengths to predict which range region the lightning stroke occurredin. If the regions predicted by the two methods are adjacent regions orthe same region then the ratio of the integrated H/E field values areused to determine the range from a look-up table.

If the two regions predicted are the near and distant regions then theratio of the total H to the total E field value is calculated from thesample data and used to determine the range from the look-up tables.

A standard deviation value for the set of elevation and azimuth anglescalculated from the sampled field values is calculated. The standarddeviation value and the range value to a lightning stroke (expressed inrectagular coordinates) is transmitted to a programmable display means.The display means then displays the lightning stroke activity as aregion of activity on a display, in accordance with its own programming.

When the apparatus of the present invention is installed in an aircraft,means for adjusting and updating the measurement of lightning strokelocation for aircraft movement (speed and heading) is provided.

The objects, features and advantages of the present invention willbecome more fully apparent from the following detailed description ofthe preferred embodiment, the appended claims and the accompanyingdrawings in which:

FIG. 1 is a preferred embodiment block diagram schematic of the presentinvention.

FIG. 2 is a more detailed block diagram of a first portion of FIG. 1.

FIG. 3 is a detailed schematic of a second portion of FIG. 1.

FIG. 4 is a more detailed block diagram of a third portion of FIG. 1.

FIG. 5 in part shows a representation of the signals of a lightningstroke, and in part is a timing diagram for a portion of FIG. 4.

FIG. 6 is a more detailed block diagram of a fourth portion of FIG. 1.

FIG. 7 is a more detailed block diagram of a fifth portion of FIG. 1.

FIG. 8 is a graph showing the relationship between the absolute value ofthe ratio of the magnetic field radiated from a lightning stroke to theelectric field so radiated versus range to the lightning stroke.

FIGS. 9a-c are an alterate block diagram embodiment of portions of FIG.4.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the preferred embodiment of the presentinvention. The apparatus comprises a pair of cross loop magnetic fieldantennas 10 and 12 and an electric field antenna 14. Since the crossloop magnetic field antenna elements have their axes perpendicular toone another, antenna 10 will be referred to as the north/south magneticfield antenna while antenna element 12 is the east/west magnetic fieldantenna. The three antenna elements are responsive to the time rate ofchange of magnetic and electric flux densities occurring because ofelectrical activity associated with lightning strikes. The signalsreceived by the antenna elements are transmitted to integratorsdesignated generally 16, 18 and 20 which provide an east/west magneticfield component, a north/south magnetic field component and a verticalelectrical field component respectively to wide band amplifiers 22, 24and 26. In the preferred embodiment, the antenna elements, theintegrators and the wide band amplifiers operate over the frequencyrange of one kilohertz (KHz) to fifteen megahertz (MHz) but otherbandwidths larger or smaller could be used.

The outputs of the wide band ampifiers 22 through 26 are provided inparallel to a sampling portion of the circuitry of the apparatus and tothe recognition circuitry portion of the apparatus. The recognitioncircuitry portion of the apparatus comprises slope detection circuitrydesignated generally 30, absolute summer circuitry designated generally32 and threshold detection circuitry designated generally 36. The outputof wide band amplifier 26 containing the vertical electric field signalis transmitted via line 27 to slope detection circuitry 30. If the risetime of this signal is less than a predetermined rise time a positivesignal is transmitted to timer circuitry designated generally 34 vialine 31. Similarly, the magnetic field signals transmitted from wideband amplifiers 22 and 24 respectively are summed vectorially in theabsolute summer circuitry 32. The output of this circuitry representsthe magnitude of the total magnetic field present at the antennaelements 10 and 12. This signal is transmitted via line 33 to thresholddetection circuitry 36 which provides a positive signal to timercircuitry 34 via line 35 if the signal exceeds a predetermined thresholdlevel. The output of the absolute summer circuitry is also transmittedvia line 39 to integrator circuitry 40 while the electric field signalfrom wide band amplifier 36 is also transmitted via line 41 tointegrator 42.

If the voltage level of the magnetic field signal from circuitry 32exceeds the predetermined threshold level of circuitry 36 and if therise time of the vertical electric field signal from wideband amplifier26 is less than the predetermined rise time of slope detection circuitry30 then the time circuitry 34 is caused to provide integration controlsignals via line 53 to the integrators 40 and 42. Integrators 40 and 42then integrate the magnetic and electric field signals over apredetermined time interval which corresponds to the most likely periodover which the lightning stroke exists. The slope detection circuitry30, the absolute summer circuitry 32, and the threshold detectioncircuitry 36, provide a means for recognizing the magnetic and electricfield signals associated with the lightning strike in the presence ofinterferring and background noise signals.

The north/south and east/west magnetic field signals are alsotransmitted over lines 55 and 57 to sampling circuitry 44 and 46respectively. The vertical electric field signal from wide bandamplifier 26 is transmitted via line 59 to sampling circuitry 48.Samples of the magnetic field and electric field signals representingthe peak of each change in the fields are taken in response to peakdetection signals provided from timer circuitry 34 over lines 43, 45 and47. Peak detection signals are generated by timer circuitry 34 inresponse to positive output signals from the slope detection circuitry30.

The samples of the magnetic and electric field signals are converted todigital signals by A/D converters in response to the peak detectionsignals. The digital signals are stored in first-in first-out (F IF O)memories. Similarly, the integrated electric field and magnetic fieldsignals from integrators 40 and 42 pass through A/D converters and arestored in F IF O memory. Together the A/D converters and F IF O memoriesare shown as preprocessing circuity 50 in FIG. 1. The peak detectionsignal for the A/D converters are transmitted thereto via line 49.

The apparatus further comprises processing circuitry means designatedgenerally 52. When the predetermined integration interval correspondingto the existence of the lightning stroke is ended the timer circuitry 34transmits an interrupt control signal via line 54 to the processingcircuitry means which in response thereto commands the first-infirst-out memories of preprocessing circuitry 50 over multiple lines 51to transmit the samples of the magnetic and electric field values andthe integrated magnetic and electric field values to a memory inprocessing circuitry means 52. This information is utilized inaccordance with the programming of the processing circuitry means tocalculate the region of activity of the lightning stroke. The resultsare transmitted to a display means which then displays the results on adisplay. The display means comprises a display processor 60 and display62. In the preferred embodiment, the processing circuitry means 52 isenabled to compensate for movement of a host platform (such as anaircraft) when determining the region of lightning activity.

Referring now to FIG. 2, further details of the integrators 16 through20 are provided. In the preferred embodiment, the north/south magneticfield antenna 10 and the east/west magnetic field antenna 12 arecommercially available antennas from EG&G Company, Models Nos. CML-7(R). The electric field antenna element 14 is an EGG Model No. FPD-2B(R). The antenna elements 10 through 14 are AC coupled throughcapacitors 202 for the magnetic field elements and capacitor 204 for theelectric field antenna 14. The integrators 16 through 20 compriseamplifiers 17, 19 and 21 (Analog Device Model No. AD509) in parallelwith filter circuitry designated generally 206 and 208 for magneticfield antennas 10 and 12 respectively and designated generally 210 forelectric field antenna element 14. The filter circuitry filters outunwanted high frequency components detected by the antenna elements andoutside the frequency band of interest. Further details on the design ofmagnetic antenna sensors and wide band integrators suitable for thepresent invention can be found in a paper by E. Philip Krider and R.Karl Noggle entitled "Broad Band Antenna Systems for Lightning MagneticFields", Journal of Applied Meteorology, Vol. 14, March 1975 herebyincorporated by reference as if specifically set forth herein. A similarcircuit is reported by Fisher and Uman, in "Measured Electric Field RiseTimes for First and Subsequent Lightning Return Strokes", Journal ofGeophysical Research, Vol. 77, Jan. 1972 which is hereby incorporated byreference as if specifically set forth heren. Selection of impedancematching devices are described in these two references and furtherinformation may be found in numerous articles on lightning measurementtechniques. The outputs from the integrators 16 through 20 are thentransmitted over lines 212, 214 and 216 respectively to single polethree throw switches 218, 220 and 222 (Analog Device Model Nos. AD7502).The output of the switches provide the weak amplified north/south andeast/west magnetic field components and the vertical electric fieldcomponents. The functioning of the switches will be described later inconnection with the processing circuitry means.

FIG. 3 shows in some detail a transistorized wide band amplifier 300 ofconventional design. It comprises at least four amplifier stages whichare directly coupled. The wide band amplifier operates over a frequencyrange from one KHz to 15 MHz and has a maximum gain of approximately sixthousand. The selection of the parameters of the wide band amplifierdepends on the type of sensors used, the electric environment andsubsequent processing circuitry. The wide band amplifier shown in detailin FIG. 3 is suitable for use as amplifiers 22, 24 and 26 in FIG. 1.Alternatively, wide band amplifiers 22, 24 and 26 can be provided usingMotorola wide band amplifiers (Model No. MWA 110,-120,-130) in acascaded circuit design. See Motorola RF Data Maual, 1980 edition, pages16-33 through 16-40 hereby incorporated by reference as if specificallyset forth herein.

Before describing FIG. 4 which shows the absolute summer circuitry 32,the slope detection circuitry 30, the level detection circuitry 36,timer circuitry 34 and integrators 40 and 42 in detail, it isinstructive to discuss the shape of the expected field voltage pulsesreceived from the wide band amplifiers 22, 24 and 26. In FIG. 5 a seriesof even numbered curved designated generally 500-506 are shownrepresenting the vertical electric field E_(V) from wide band amplifier26, the H_(NS) field voltage from wide band amplifier 24, the H_(EW)field value from wide band amplifier 22 and the absolute magnitude ofthe combined magnetic field, respectively H. The ordinate in each curverepresents voltage amplitude in millivolts while the abscissa representstime in microseconds. Inspection of the curves show that the H and Efield voltages associated with a single lightning stroke (many strokescomprises a lightning flash) usually last about one hundredmicroseconds. Much research in the nature of electrical signals arisingfrom lightning strokes indicates that almost all vertical electric fieldvoltages (E_(V)) will have an initial rise time (see 507 on curve 500)of less than five microseconds, and that the pulse will contain aplurality of randomly placed smaller pulses or peaks of submicrosecondduration and rise times of less than five microseconds. See for examplepositive slopes 508, 510, 512 etc. on curve 500 in FIG. 5. Therecognition circuitry of FIG. 4 takes advantage of these characteristicsto cooperate with the control circuitry portion of FIG. 4 to furnishcontrol signals for integrating and sampling the E and H field voltages.

Referring now to FIGS. 1 and 4, the absolute summer circuitry designatedgenerally 32 connected to the H_(EW) and H_(NS) wide band amplifiers 22and 24 on lines 402 and 404 respectively comprises a pair of firstcircuitry portions designated generally 406 and 408 and an outputoperational amplifier 409. Capacitors 410 and 412 block unwanted DCcomponents from the first circuitry portions 406 and 408 but pass thepulses magnetic field voltages H_(NS) and H_(EW).

First circuitry portion 406 (which is identical to circuitry portion408) comprises an operational amplifier 414 and switching circuitrydesignated generally 416. If the H_(NS) field voltage is negative thenoperational amplifier 414 switches resistors 405 and 413 into thecircuit at the output of 409. This has the effect of inverting theH_(NS) voltage. If H_(NS) is positive the switching circuitry 416by-passes the resistors 405 and 413 and the output is through resistor407. In this manner only the absolute magnitudes of the H_(NS) andH_(EW) field voltages are delivered to operational amplifier 409 oversingle input line 418.

The combined magnetic field voltage from operational amplifier 409 isthen transmitted to operational amplifier 420 via the line 33 (see alsoFIG. 1). Operational amplifier 420 is biased to a predetermined negativethreshold voltage. Unless the combined magnetic field voltage exceedsthe magnitude of the threshold voltage, operational amplifier 420provides a low output. The biased operational amplifier 420 provides thethreshold detection function of threshold detection circuitry 36. Curve506 in FIG. 5 represents the total magnetic field signal transmittedfrom operational amplifier 409.

The vertical electric field voltage E_(V) is transmitted from wide bandamplifier 26 via line 27 (see FIG. 1) and then lines 425 and 426 throughDC blocking capacitors 427 and 428 to the slope detection circuitrydesignated generally 30. Slope detection circuitry 30 comprises twoparallel similar circuits designated generally 430 and 432. Circuitry430 comprises operational amplifier 434 (Analog Device Model No. AD 509)with two inputs 435 and 436. Input 435 is connected to input 436 viaresistor 437 and input 436 is connected to ground through capacitor 438.Operational amplifier 434 will provide a positive output voltage toinverter 446 whenever the field voltage E_(V) increases faster thancapacitor 438 can charge through resistor 437. The product of resistor437 and capacitor 438 determines the sensitivity of the slope detectioncircuitry. For the preferred embodiment, this product is set to 62microvolts per second thus allows only the submicrosecond lightningpulses to be detected. Input 436 has a positive voltage bias throughresistor 439 and the ratio of resistors 437 and 439 sets the minimumsignal level which the slope detection circuit will detect. Thepreferred embodiment is set at 2 millivolts.

Similarly, circuitry 432 comprises operational amplifier 440 (AnalogDevice Model No. AD509) and it will provide a positive output toinverter 448 whenever field voltage E_(V) decreases faster thancapacitor 442 can charge through resistor 444. Either a positive ornegative voltage change of E_(V) having the correct rise time asfunctionally defined by circuitry 430 and 432 will provide a positiveinput to inverter 446 or 448. If no fast rise time occurs, the outputsof operational amplifiers 434 and 440 will be low triggering a highoutput from inverters 446 and 448. Examples of submicrosecond pulseswhich will trigger the above described circuitry is shown as slopes 507,508, 510 and 512 in FIG. 5.

The outputs of inverters 446 and 448 are furnished as inputs to NANDgate 450. In the absence of any fast rise time pulses from wide bandamplifier 26, the outputs of the inverters are high and NAND gate 450output is low. When a slope of the proper rise time (either positive ornegative) occurs on the E_(V) voltage pulse 500 one of inverters 446 or448 will go low causing the output of NAND gate 450 to go high until thepeak voltage on the pulse on curve 500 is reached and then the output ofNAND gate 450 will go low. See FIG. 5, curve 514, where the output ofNAND gate 450 is shown as a series of pulses 516 corresponding to fastrise time on the E_(v) signal 500.

The output of NAND gate 450 is transmitted via line 452 to NAND gate 454and line 456 to NAND gate 458. A flip flop 460 is provided and its Qoutput is transmitted to NAND gates 454 and 458 as a high gating signal.NAND gate 458 also receives the output of operational amplifier 420 fromthreshold detection circuitry 32 via line 35 as a third input.

When the processing circuitry means 52, (see FIG. 1) clears flip flop460 with a data clear signal via line 459a (after it has finished takingdata from preprocessing circuitry 50) a high signal is transmitted from460 Q to NAND gates 454 and 458 enabling them. When a low signal istransmitted to NAND gate 450 (indicating a fast rise time) it transmitsa high to NAND gate 454 and 458. If at the same time, thresholddetection operational amplifier 450 transmits a high to NAND gate 458,NAND gate 458 will transmit a low signal to one shot 462 which uponreceiving the low signal will generate or transmit a one hundredmicrosecond long low signal at its Q output 463. See signal 517 of FIG.5 for the 100 microsecond low signal. This low signal is transmitted vialine 464 to a low enable input of one shot 468.

Whenever slope detection circuitry 30 provides a low signal input toNAND gate 450 in response to a fast rise time pulse on signal 500, NANDgate 450 transmits a high signal to NAND 454. If the Q output from flipflop 460 is also high then NAND gate 454 will transmit a low signal toone shot 468 as long as the output from gate 454 remains high. (Thisoutput remains high until the fast rise time pulse from widebandamplifier 26 peaks and then it returns low.) As the signal from NANDgate 450 returns low, the output of NAND gate 454 will go high as thiswill trigger one shot 468 (as long as the low enable input is low) togenerate a 250 nanosecond pulse on line 465 on the leading edge of thehigh signal from NAND gate 454. This 250 nanosecond high signal is oneof the control signals generated by timer circuitry 34 and is called thepeak detection signal. Peak detection signals occur even when a positivethreshold signal from operational amplifier 420 is absent as long as oneshot 468 is enabled by the one hundred microsecond pulse from 462Q. Thepeak detection signals are shown on curve 518 of FIG. 5. Note that theyoccur on the falling edge of the NAND gate 450 high signal which is thesame as the leading edge of the high going signal from NAND gate 454.

The total magnetic field from absolute summer circuitry 32 is alsotransmitted via line 39 (see FIG. 1) to integrator 40 which comprises aninput switch 471 and integrator circuitry designated generally 478 inparallel with a second switch 481. Integrator circuitry 478 comprises anoperational amplifier 479 in parallel with a capacitor 480. The outputof switch 471 is connected to the input of the parallel arrangement ofintegrator circuitry 47 and second switch 481. The vertical E fieldcomponent from wideband amplifier 26 is also transmitted through DCblocking capacitor 474 over line 41 to an integrator 42 which isidentical in design to the integrator 40. Input switches 471 arenormally open but they are switched to closed by the one hundredmicrosecond low signal from one shot 462 Q along lines 475 and 476. Whenthe switches are closed, the E_(V) and H field voltages are transmittedto integrator circuitry 478.

The second switch 481 in each circuit is normally closed and provides analternate path to the integration circuitry 478. However, the low onehundred microsecond pulse 517 from one shot 462 is also connected to oneshot 485. Upon receiving it, one shot 485 on the falling edge of the lowsignal 517 generates and transmits a high two hundred microsecond pulse(see diagram 520 of FIG. 5) over lines 486 and 487 to switches 481 toopen them.

When input switches 471 are open, closed second switches 481 provide ameans for keeping integrator circuitry 478 from saturating on inputnoise. Switches 481 open when switches 471 close but switches 481 remainopen for 100 microseconds after switches 471 open to allow the H andE_(v) integrated signals to be transmitted to preprocessing circuitry 50in FIG. 1. The one hundred microsecond 462 Q signal to switches 471 and485 Q signal to switches 481 are control signals controlling theintegration of the E and H field voltages over the one hundredmicrosecond interval.

Finally, the Q output of one shot 462 is connected via line 490 to flipflop 492. When the one hundred microsecond interval is over and 462 Qgoes high it sets flip flop 492 causing a high signal to be transmittedvia line 54 to the processing circuitry means 52 as an interrupt signal(see diagram 522 in FIG. 5). At the same time, flip flop 492 Q goes lowan is transmitted via line 495 as an inhibit data measurement signal toflip flop 460 setting it and causing 460 Q to go low. The low signaldisables NAND gates 454 and 458 while the processor circuitry means 52interrogates preprocessing circuitry 50 for the sampled and integrated Eand H field voltages (see diagram 524 in FIG. 5 for the inhibit datameasurement signal). When the processing circuitry means 52 has finishedinterrogating the preprocessing circuitry 50, it transmits a clearsignal to flip flops 460 via line 459a (see diagram 530 in FIG. 5) and492 via line 459b (see diagram 526 in FIG. 5) which results in enablinggates 454 and 458 and disabling the high interrupt signal 54 to theprocessing circuitry means 52 from flip flop 492.

All of the operational amplifiers shown in FIG. 4 are Analog DeviceModel No. AD509 amplifiers. Switches 471 and 481 are Analog Device ModelNo. AD7513 switches. The remaining logic and circuit components areeasily recognized and commercially available components.

FIG. 6 shows the electric (E_(V)) and magnetic (H_(NS) and E_(EW)) fieldsampling circuitry designated generally 44, 46 and 48 and preprocessingcircuitry 50 of FIG. 1 in more detail. Capacitors 602, 604 and 606 blockunwanted DC components from the signals E_(V), H_(NS) and H_(EW)respectively furnished over lines 59, 55 and 57 but pass the pulsedfield voltages. The field voltages are then transmitted through delaycircuitry 608 a, b and c (Harry J. White Co. Model No. MD600201K) beforebeing forwarded to track and hold circuitry 610 a, b and c. The trackand hold circuitry (Model No. HTC-0300 MM, made by Analog Devices) inresponse to the peak detection control signals from one shot 468 overline 465 holds the peak field voltage constant. The voltage held bytrack and hold circuitry 610 a, b and c is the peak voltage occurringafter a five microsecond or less rise time in the E_(V) voltage 500.(see the slopes 507, 508, 510 and 512). There is some delay of the peakvoltage as it passes through the circuitry of FIG. 4 before a peakvoltage detection control signal is generated. To accommodate thisdelay, delay circuitry 608 a, b and c is added. In the preferredembodiment, about six hundred nanoseconds of delay is required.

Each peak field voltage signal held by track and hold circuitry 610 a, band c is converted to a digital signal by A to D (A/D) converters 612 a,b and c in response to the falling edge of the peak detection signalfrom line 465 and causes a low signal on lines 634 a,b and c and 638 a,band c. In the preferred embodiment, the A/D converters 612 a,b and c areDatel-Intersil devices, Model No. ADC817MM, which converts the signalinto a twelve bit digital signal in 2.5 microseconds when the conversionis complete. A/D converters 612 a,b and c then transmits a high signalover lines 634 a,b and c which causes the digital sampled peak fieldvoltage to be clocked into the first-in first-out (FIFO) memories 614a,b and c where they are stored until called for by the processingcircuitry means 52. As described earlier, each peak signal on waveform500 (E_(V) ) in FIG. 5 which has a rise time less than equal to fivemicroseconds causes a peak detection signal which then causes a sampleof the E_(V), H_(NS) and H_(EW) field signals to be taken and stored inFIFOs 614 a,b and c during the one hundred microsecond interval (signal517 in FIG. 5) generated by one shot 462 Q in FIG. 4. In the preferredembodiment, FIFOs 614 a,b and c are Advanced Micro Devices, Model No. AM2812A.

When the A/D converters generate rising edge signals over lines 634 a,band c and transmit the twelve bit digital signals to FIFO memories614a,b and c, they also transmit high data ready signals to AND gate 616over lines 638a,b and c. AND gate 618 transmits a high data ready signalover line 618 to one shot 468. This enables one shot 468 to generate anew peak detection signal. If the data ready signal were not used toenable 468 a second closely occurring peak voltage signal on waveformE_(V) would generate a second peak detection signal causing the A/Dconversion process of the first sample signal to be interrupted.

An alternate embodiment for implementing the integration of the total Hand E field voltages requires modifications to FIG. 4 and is describedin block diagram form in FIGS. 9a,b and c. A true RMS measurement of theH_(EW), H_(NS) and E_(V) field voltages are made accurately by acommercially available device Analog Devices Model No. AD536. Thepreferred embodiment implements the auxiliary dB output of the AD536A asdescribed in the Analog Devices Data Acquisition Products Catalog, 1978edition, pages 229-234 hereby incorporated by reference as ifspecifically set forth herein. Input to the RMS converters 900a,b and care from switches 901a,b and c which are identical to the switches 471described in FIG. 4. One shot 462Q in FIG. 4 transmits a low 100microsecond pulse to switches 901a,b and c over lines 904a,b and cclosing them and allowing RMS converters 900a,b and c to integrate theH_(EW), H_(NS) and E_(V) field voltages. At the same time high signal462Q opens switches 903a,b and c via lines 906a,b and c. Openingswitches 903a,b and c sets the RMS converters 900a,b and c to a knownvoltage level (ground for preferred embodiment) before starting the 100microsecond integration. The outputs of RMS converters 900a,b and cconnect to Sample and Hold (S/H) circuitries 902a,b and c. The 100microsecond low signal from 462Q is also connected to S/H circuitries902a,b and c via lines 900a,b and c. On the rising edge of the lowsignal, the (S/H) circuitries 902a,b and c hold the integrated voltageswhile the processing circuitry means converters and stores them asdigital data. The S/H circuitries 902a,b and c for the preferredembodiment are Harris Corporation Model No. HA-2420-8 devices.

With the alternate embodiments of FIG. 9a, the total H field is notavailable as an analog voltage. The threshold detection signal foramplifier 420 is provided by connecting the E_(V) field voltage theretovia line 911 which is connected to line 27. See FIG. 9b. Finally, inFIG. 9c, output lines 912a,b and c from S/H circuitries 902a, b and care provided to the multiplexer circuitry 636 of FIG. 6. The lines912a,b and c will now represent the dB RMS voltage of the H_(EW), H_(NS)and E_(V) fields. The multiplexing and A/D conversion of these signalsare similar to that described hereinafter for the integrated E and Hfields on lines 66 and 68 in connection with the description of FIGS. 6and 7.

The processing circuitry means 52 is described in block diagram form inFIG. 7. The processing means comprises the controller 56, random accessmemory 702, read only memory 704, random access memory 706, arithmeticprocessing unit 707, and an address data bus 710. The various portionsof the processing circuitry means 52 are connected together by theaddress/data bus 710.

The processing circuitry means is programmable and the programs arestored in ROM 704. After the processing circuitry means has finishedprocessing data and is ready to receive new data from a new lightningstrike it transmits a data clear signal (see diagram 530 in FIG. 5) toflip flops 460 and 492 in FIG. 4 over lines 459a and b. Lines 459a and459b are shown connected to the random access memory 706. When alightning strike is recognized by the circuitry of FIG. 4, a one hundredmicrosecond integration and sampling time is set by the low output ofone shot 462Q as described earlier. When this one hundred microsecondinterval is over the change in state of the output of one shot 462 setsflip flop 492 providing an interrupt signal 522 over line 54 to thecontroller 56.

The processing circuitry means is now ready to read the data via bus 712through the read only memory 704. The data to be read are the sampledE_(V) and H_(NS) and H_(EW) field values stored in the FIFOs 614 and theintegrated E_(V) and magnetic field values transmitted from integrators40 and 42 (or, alternatively, S/H circuitries 902a,b and c). Toaccomplish this the processing circuitry means transmits sample datacontrol signals (see diagrams 526, 528 in FIG. 5) over lines 51 (FIG. 1)which comprise even numbered control lines 716 through 624 (FIGS. 6 and7) from the read only memory 704. Signals 720 and 722 are transmitted todecoder 620 of FIG. 6 which in turn provides interrogation signals overlines 622,624 and 626 to tri-state buffers 628,630 and 632 (Intel DeviceNo. M8212) respectively. The tri-state buffers 628 through 632 areconnected to FIFO 614a, b and c respectively.

Control lines 716 and 718 from read only memory 704 are connected tomultiplexer 636 of FIG. 6. Multiplexer 636 (Analog Device No. AD7502) isconnected between track and hold circuitry 610 c of H_(EW) samplingcircuitry 46 and A/D converter 612c. The integrated vertical electricfield from integrater 42 of FIG. 1 is transmitted via line 66 tomultiplexer 636 while the integrated magnetic field from integrator 40is transmitted via line 68 to multiplexer 636 in response to commandsignals transmitted over lines 716 and 718. (See also FIGS. 9a through9c). The processing circuitry means transmits an A/D convert commandover line 724 to A/D converter 612c via OR gate 642. At the completionof an A/D conversion the digital data is transmitted to FIFO 614c.

Assuming that the circuitry of FIG. 4 is cleared to accept data from alightning strike, when a lightning strike occurs that is recognized bythe circuitry of FIG. 4, a one hundred microsecond pulse is transmittedfrom one shot 462 in a manner as described previously. As the onehundred microsecond interval ends flip flop 492 is set and a highinterrupt signal is transmitted therefrom via line 54 to the controller56. This signal initiates a sample data interrupt program stored in ROM704. The sample data interrupt program transmits an address signal vialines 716 and 718 to multiplexer 736 and a command signal via line 724to read the integrated vertical electric field value over line 66 intoA/D converter 612c where it is converted into digital form. Next theaddress over lines 716 and 718 is changed so that multiplexer 636 readsthe integrated magnetic field value from line 68 into A/D converter 612cwhere it is converted into digital form. (In FIGS. 9a-9c, three separateaddresses on lines 716 and 718 are required to read the integratedH_(NS), H_(EW) and E_(V) fields on lines 904a,b and c). From A/Dconverter 612c the digital values of the electric and magnetic fieldsare transmitted to FIFO 614c on the rising edge of control line 634c.Next control signals are transmitted from read only memory 704 via lines720 and 722 to decoder 620. Decoder 620 transmits a signal via line 624to tri-state buffer 630 and processing circuitry means transmits a readsampled H_(NS) data signal over line 728 to FIFO 614b. The data in FIFO614b is then read via line 712 into the read only memory 704 and isstored in RAM 706. When all the data has been read from FIFO 614b, thesignals via lines 720 and 722 are changed by the processing circuitrymeans so that decoder 620 transmits a signal via line 626 to tri-statebuffer 632. A read sampled H_(EW) data signal over line 726 from theprocessing circuitry means 52 causes the sampled H_(EW) data stored inFIFO 614c to be transmitted via line 712 into read only memory 704 andstored in RAM 706. Finally, the signals via lines 720 and 722 from readonly memory 704 are changed and the decoder 620 transmits a signal vialine 622 to tri-state buffer 628 which then reads the sampled E_(V) datain FIFO 614a along with the integrated E_(V) and H field values oncommand from processing circuitry means via line 730. These also arestored in RAM 706. When all the data has been read from the FIFO 614a,band c a Sampled Data Program is called for.

The Sample Data Program also stored in ROM 704 utilizes the sampled andintegrated E and H field values of the lightning stroke to calculate thedirection and to measure the range of the lightning activity.

The direction is calculated in terms of an elevation angle θ existingbetween the location of the lightning stroke and the antennas 10, 12 and14; and an azimuth angle φ existing between the location of thelightning and the same antennas. As described earlier, each fastrisetime pulse present in the lightning stroke triggers the circuitrydescribed earlier to sample the E and H fields radiated by the lightningstroke. For each sample taken (where each sample corresponds to onepulse in the lightning stroke), three values E_(V), H_(NS) and H_(EW)are measured by the three antenna elements. For one lightning stroke inthe preferred embodiment, a maximum of 30 sets of three sampled fieldvalues are measured and stored during the first 100 microseconds.

As described earlier, the sampled field values are related by theequation, ##EQU1##

This equation in two unknowns can be solved by using two differentthreesomes of the sampled field values in the set. For example, ##EQU2##Since the Sin θ must be less than 1, the bracketed expression above onthe right side of the equation opposite θ must also be less than 1. Ifit is not the calculated θ and φ values are invalid. The Sample DataProgram using the equations above for θ and φ calculates θ and φ usingtwo threesomes of sampled field values from the set of sampled fieldvalues stored for each lightning stroke. The Sample Data Programcalculates θ and φ a plurality of times for each possible combination oftwo different threesomes found in the set (maximum of 30 for preferredembodiment). Each time the Program calculates a θ and φ pair it checksits validity as described above. In general, all pairs of θ and φ willnot agree exactly.

The Sample Data Program calculates the centroid value from the pluralityof θ and φ's calculated. This is the direction angle to the lightningstroke from the equipment. Next, the Program calculates the standarddeviation of the set of calculated elevation and azimuth angles, θ andφ. Later it will be seen that the centroid value of θ will be used toconvert the range to the projected distance on the ground to thelightning stroke. The standard deviation will be used to display thelightning activity as a region of activity rather than an isolatedpoint. The standard deviation is stored in RAM 702.

The absolute value of the ratio of the magnetic field, H, to theelectric field, E, (|H/E|) varies in a predictable way with the rangefrom the lightning stroke. See FIG. 8. FIG. 8 is separated into threerange regions: the near region 800 from 0 to 10 kilometers; the midregion 802 from 10 kilometers to 50 kilometers; and the far region 804from 50 kilometers and greater. Note that |H/E| peaks in value at about50 kilometers and that it is possible to have range ambiguities forvalues of |H/E| near the peak, i.e., for a given value of |H/E| near itspeak value two possible ranges are possible, one in the far range 804and one in the mid range 802.

The Sample Data Program, stored in ROM 704, first calculates the meanvalue of the H_(NS) field components for the lightning stroke inquestion from the sampled components of H_(NS) that had been stored inFIFO 614b and stored in RAM 706 of the processing means. Then in similarfashion H_(EW) is calculated (from the sampled values of H_(EW) that hadbeen stored in FIFO 614c). A total value, P, for the magnetic field iscalculated by adding H_(NS) to H_(EW).

A magnetic or electric field radiated from a lightning stroke is assumedto have an initial amount of energy associated therewith. This energyattenuates as the E and H fields travel farther from the source of thelightning stoke. For example, at ten kilometers from the stroke theexpected energy of the E and H fields is the initial energy minus theamount of attenuation occuring in ten kilometers. This energy can beassigned a value, K1. At 50 kilometers the expected value is K2. Todetermine a rough estimate, TA, of the range of the lightning strike andto help resolve the ambiguity present in the curve of FIG. 8, the SampleData Program compares P with K1 and K2. If P is greater than K1 then thelightning stroke is close and the near range of curve 800 is used. If Pis greater than K2 then the mid range is used; otherwise, the lightningstroke is in the far range.

The Sample Data Program compares the total power in the H field from thelightning stroke (as calculated from the samples of the H field storedin FIFO's 614b and 614c) with first set of predetermined range values K1and K2 as described above.

This estimate is called TA. In a similar manner, the Sample Data Programtakes the integrated H field value (as integrated by integrator 40;multiplexed by multiplexer 636; converted by A/D converter 612c; andstored in FIFO 614c until transmitted to memory 54 of the processingmeans) and compares it with a second set of predetermined range valuesK3 and K4. This comparison is used as before to estimate which rangeregion the associated lightning stroke occured in. This estimate iscalled TH. The constants K1 and K2 differ from K3 and K4 because the K1and K2 values are used with the peak sampling circuitry 44,46 and 48.The field samples measured thereby are high frequency samples of theligntning and thus are weaker at greater distances from the strike thanthe integrated field values which are mainly a measurement of the lowfrequency component of lightning. Hence, the constants K3 and K4 differfrom K1 and K2.

The two estimates of range (TA and TH) are examined by the Sample DataProgram to see if they agree. If the two estimates of range differwidely, that is, if one estimates is for the far range region and one,near range region, then the integrated vertical electric field (asinputted from integrator 42 in FIG. 1 through multiplexer 636, A/Dconverter 612c and FIFO 614c in FIG. 6) is used to estimate range bycomparison with a third set of predetermined range values K5 and K6.This estimate is called TE. Values of K5 and K6 are determined bypredicting the signal strength of an average lightning strike with thehigh frequency energy value as removed by the integrator 42. If the twoestimates of range region TA and TH based on H field values are notwidely different or agree then the Sample Data Program will form the|H/E| ratio, which will provide an accurate determination of range fromFIG. 8, by using only the integrated values of the H and E_(V) fieldsformed by integrators 40 and 42 respectively.

In the case where the estimates of range TA and TH differ widely, theestimate of range region based on the integrated E_(V) field TE iscompared separately with the TA estimate and with the TH estimate. If TEagrees with either TH or TA an error is presumed in the data measured bythe circuitry. If TE is different from TA or TH then the |H/E| ratiowill be formed using the field power calculated from the sampled valuesof the field. Of course, the Sample Data Program must first calculatethe mean value of E from the sample values of E that were stored in FIFO614a before being inputted to memory 54.

When the embodiment of FIGS. 9a through 9c is used the db value of theRMS field strengths for H_(NS), H_(EW) and E_(V) are used in place ofthe integrated E and H field values provided via lines 66 and 68.

The near, mid and far range regions versus |H/E|, even numbers 800through 804 respectively of FIG. 8, are stored as a set of three tablesin memory. The |H/E| value formed by the Sample Data Program usingeither the integrated field values or the sampled field values iscompared with the appropriate table to determine the correspondingrange, R, of the lightning activity. This value of R is the truedistance from the measuring apparatus to the lightning stroke.

It should be understood from the above description of the Sample DataProgram thus far, that the method and apparatus of this inventionprovides circuitry and microprocessing power which uses a great deal ofthe detailed electromagnetic field information resulting from a lightingstrike to determine accurately the range and region of activity of thelightning strikes relative to the equipment.

It is desirable to know the ground distance, D, between the observingequipment and the lightning activity. D is related to R by the Sin ofthe elevation angle θ, that is,

    D=R Sin θ

The Sample Data Program will convert R to D using the centroid value ofθ calculated earlier by the Program. However, D is set equal to R whereR is determined from the table corresponding to the far range regionsince for lightning strikes that far away (greater than 50 kilometers) θis small and Sin θ approximately equals one.

Now that the direction and distance of the storm relative to theobserving equipment is calculated it must be displayed. But first, thedistance calculated thus far must be adjusted for the range scale factorwhich is controlled by a thumb wheel switch 736 in FIG. 7. This manualselection of scale factor is monitored via lines 739 and 738 by theSchedule Routine Program stored in ROM 704. The Schedule Routine Programis executed by controller 56 every 10 milliseconds. A detaileddescription of the design using the INTEL 8085A for a minimum system isfound in INTEL Component Data Catalog, 1980 edition, pages 6-9 through6-24, hereby incorporated by reference as if specifically set forthherein. The controller 56 is interrupted once every 10 milliseconds byRAM 702 (the INTEL Component Data Catalog completely explains the sue ofthe timer output connection). The Schedule Routine Program firstdetermines if 0, 200, 500, 700 and 900 milliseconds (10 interrupts fromRAM 702 equals 100 milliseconds) has been completed. At the 0millisecond time the range input lines are monitored over lines 738 and739 and a signal transmitted over lines 744 and 746 which are used toadjust the switches 218, 220 and 222 in FIG. 2 to a desired input signallevel that does not over saturate the circuitry or increases theapparatus sensitivity to distant lightning strikes. This range scalefactor is stored in RAM 702 and is used to offset the range calculatedby the Sample Data Program. The Schedule Routine Program calculates thetrue range on every 900 millisecond count and updates the display. Thisis accomplished by transmitting the x and y rectangular coordinates ofthe lightning and the standard deviation to the display processor 60 fordisplay on the display means 62. The x and y coordinates are related toD and the centroid value for φ as follows:

    x=D·Sin φ

    y=D·Cos φ

x and y is stored in RAM 702.

The display processor is programmable and the information provided to itcan be displayed and the display updated in a variety of ways. Displaysystems including a display processor, a display under the control ofthe display processor and programs for use by the display processor arecommercially available along with an interface for accepting theinformation to be displayed. One such display system suitable for usewith the present invention is a DIGITUS Corporation Rainbow 2000 System.See in particular DIGITUS Corporation users Manual which is herebyincorporated by reference as if specifically set forth herein.

One such program shows the equipment at the origin of the display withazimuth angle varying 360° about the origin. Distance is shownincreasing along radials from the origin. The farther away the lightningstroke is the farther away from the origin is the indication. Theuncertainty in precise distance is shown as a circle based on the valueof the standard deviation of the set of θ's and φ's. It is clear fromthe design thus far, the range scale can be varied by the thumb wheel736.

The programs also allows for variations in how often the display isupdated with new information; how long old information is retained; andthe use of color or intensity to differentiate between intensity levelsof the storm based on similarities between old and new information aboutthe lightning activity.

The ability to locate and track electrical activity by aircraft isextremely important. In an aircraft the lightning activity is displayedrelative to the heading of the aircraft. The nose of the aircraft pointsat zero degrees azimuth. However, the speed and direction of aircraftflight constantly changes the location of the lightning activityrelative to the aircraft. To compensate for this the processing means isprogrammed with a Schedule Routine Program previously discussed in aboveparagraph, which updates the x and y coordinates of lightning activitypreviously displayed. Heading information from the aircraft'snavigational system is transmitted via a plurality of lines 732 tosynchro to digital converter (S/D) 740 in FIG. 7. The headinginformation is analog in nature which the synchro to digital device 740converts to digital data when processing circuitry means transmitts acommand over line 734. Model No. HXDC 10-L-3 made by ILC Data DeviceCompany, can be used as the S/D.

The change in azimuth display, φ, is calculated by the Schedule RoutineProgram on the 900 millisecond count by subtracting the previous headingfrom the newest. The change in x and y coordinates of previouslydirected, analyzed and displayed lightning activity (x and y) iscalculated by using the calculated centroid value of φc:

    x=Speed·Sin φc

    y=Speed·Cos φc

where speed is the known speed of the aircraft stored in ROM 704 withvalue set in accordance to type of aircraft. For example, a Cessna 182as a nominal cruising speed of 120 NM. In the preferred embodiment thedisplay is updated every second.

However, the Sample Data Interrupt and Sample Data Programs will operatewhen triggered by randomly occuring lightning strokes. These will notalways occur every tenth of a second when heading is being updated. Itis desirable to use the latest heading information possible. Betweendisplay updates (every second) the Schedule Routine Program samplesheading at 200, 500, 700 and 900 milliseconds, The Sample Data Programwill use the latest heading information available when firstcalculating, θ, φ and R and then will update the heading to correct thex and y coordinates before transmitting them to the display. As anexample, suppose a lightning strike occurs at 450 milliseconds after thelast display update by the Schedule Routine Program. The latest headinginformation available to the Sample Data Program is the headinginformation at 200 milliseconds. This information will be used by theSample Data Program to calculate θ, φ etc. However, it takes the SampleData Program more than 50 milliseconds to acquire and calculate theinformation. This means that by the time the information (x and ycoordinates) are ready for transmission to the display processor, theSchedule Routine Program has provided a new heading at 500 milliseconds.So, the Sample Data Program updates the newly measured and calculated xand y coordinates for the new heading using the following equations:

    φ=Heading (500 milliseconds)- Heading (200 milliseconds)

    x=Speed·Sin φ

    y=Speed·Cos φ

    x=D·Sin φ+x

    y=D·Cos φ+y

The display means will display x, y and the standard deviation of allcalculated lightning strikes which occured since last one second update.

While the present invention has been disclosed in connection with thepreferred embodiment thereof, it should be understood that there may beother embodiments which fall within the spirit and scope of theinvention as defined by the following claims

I claim:
 1. An apparatus for determining the location of lightningstrokes, each lightning stroke generating electric (E) and magnetic (H)field components, said apparatus comprising:receiving means forreceiving separately the electric (E) and magnetic (H) field componentsof a lightning stroke and for generating electrical signals associatedwith said E and H field components; recognition circuitry meansconnected to said receiving means for indicating when said E and H fieldcomponents of a lightning stroke have been received by said receivingmeans; control circuitry means connected to said recognition circuitrymeans for providing control signals to said apparatus when saidrecognition circuitry means indicates that said E and H field componentsof a lightning stroke have been received by said receiving means;integration circuitry means connected to said receiving means and saidcontrol circuitry means for integrating separately over a predeterminedtime interval said electrical signals associated with said E field andsaid electrical signals associated with said H field, said integrationoccurring in response to at least a selected one of said controlsignals; sampling circuitry means connected to said receiving means andsaid control circuitry means for sampling said electrical signals inresponse to a plurality of second ones of said control signals; andprocessing circuitry means disposed to receive said integrated andsampled electrical signals in response to a third one of said controlsignals, said processing circuitry means for determining the directionto said lightning stroke relative to said apparatus from said sampledelectrical signals, and for determining the distance to said lightningstroke from said apparatus from said integrated or sampled electricalsignals.
 2. The invention of claim 1 wherein said apparatus furthercomprises display means connected to said processing means fordisplaying the distance and direction to said lightning stroke.
 3. Theinvention of claim 1 wherein said apparatus further comprisespreprocessing circuitry means connected to said sampling circuitrymeans, said control circuitry means and said processing circuitry meansfor converting said intergrated and sampled electrical signals intodigital signals for transmission to said processing circuitry means. 4.An apparatus for determining the location of lightning strokes, eachlightning stroke generating electric (E) and magnetic (H) fieldcomponents, said apparatus comprising:receiving means for receivingseparately the electric (E) and magnetic (H) field components of alightning stroke and for generating electrical signals associated withsaid E and H field components; recognition circuitry means connected tosaid receiving means for indicating when said E and H field componentsof a lightning stroke have been received by said receiving means;control circuitry means connected to said recognition circuitry meansfor providing control signals to said apparatus when said recognitioncircuitry means indicates that said E and H field components of alightning stroke have been received by said receiving means; integrationcircuitry means connected to said receiving means and said controlcircuitry means for integrating separately over a predetermined timeinterval said electrical signals associated with said E field and saidelectrical signals associated with said H field, said integrationoccurring in response to at least a selected one of said controlsignals; and sampling circuitry means connected to said receiving meansand said control circuitry means for sampling said electrical signals inresponse to a plurality of second ones of said control signals.
 5. Theapparatus according to claim 1 or 4 wherein said receiving meanscomprises: an electric field antenna element for receiving the electricfield component of said lightning stroke; and a pair of magnetic fieldantenna elements for receiving orthogenal components of the magneticfield components of said lightning stroke.
 6. The apparatus according toclaim 1 or 4 wherein each of said electrical signals has an initial risetime and associated subsequent sub pulse rise times and wherein saidrecognition circuitry means further comprises: rise time circuitry meansfor providing a rise time signal to said control circuitry meanswhenever said initial rise time and said sub pulse rise times of saidelectrical signal associated with said E field component is less than apredetermined rise time value; and threshold detection circuitry forproviding a threshold signal to said control circuitry means whenever apreselected one of said electrical signals exceeds a predeterminedthreshold value.
 7. The invention of claim 6 wherein said controlcircuitry means generates said at least a selected one of said controlsignals when said rise time signal and said threshold signal occursubstantially simultaneously.
 8. The invention of claim 7 wherein saidcontrol circuitry means transmits said second ones of said controlsignals to said sampling circuitry means in response to said rise timesignals only during the presence of said first control signal occurringduring said integration predetermined time interval.
 9. The invention ofclaim 6 wherein said predetermined rise time value is less than or equalto five microseconds.
 10. The invention of claim 7 wherein saidintegration predetermined time interval is substantially between 100microseconds and 200 microseconds.
 11. The apparatus according to claim1 or 4 wherein said sampling circuitry means comprises: track and holdcircuitry means disposed to receive said electrical signals from saidreceiving means and hold said electrical signals at a constant voltagelevel in response to said second control signals; and delay circuitrymeans connected between said receiving means and said track and holdcircuitry means for delaying transmission of said electrical signals tosaid track and hold circuitry means by a predetermined delay valuewhereby said track and hold circuitry holds peak values of saidelectrical signals.
 12. The apparatus according to claims 1 or 4 whereinsaid integration circuitry means comprises:true root mean squarecircuitry means disposed to receive said electrical signals from saidreceiving means for providing output signals in response to said atleast a selected one of said control signals, said output signals havingamplitudes which are the logarithm of the root mean square of saidelectrical signals; and sample and hold circuitry means connected tosaid true root mean square circuitry means for receiving said outputsignals and holding said signals at a constant voltage level in responseto said at least a selected one of said control signals.
 13. Theinvention of claim 3 in which said preprocessing circuitry means furtherincludes analog to digital (A/D) converter means disposed to receivesaid sampled and integrated E and H field components for providing aplurality of digital signals.
 14. The invention of claim 13 wherein saidpreprocessing circuitry means further comprises: memory means andincluding second logic connected to said A/D converter means and saidprocessing circuitry means for determing when integrated and sampledelectrical signals are available for storage in said memory means;andstorage means for storing said integrated and sampled electricalsignals.
 15. The apparatus of claim 14 wherein said storage meansincludes a plurality of first-in-first-out (FIFO) memories.
 16. Theapparatus of claim 15 which further includes a third logic meansconnected to said storage means and said processing circuitry means forreading out said integrated and sampled electrical signals from saidstorage means for processing by said processing means.
 17. A method oflocating and tracking lightning strokes each stroke havingelectromagnetic radiation associated therewith comprising the stepsof:receiving separately a component of said electric (E) field and firstand second orthogonal components (H₁ and H₂) of said magnetic (H) fieldassociated with a lightning stroke; generating electrical signalsassociated with said E, H₁, and H₂ field components, said electricalsignals characterized by an initial risetime less than a predeterminedrisetime value and having associated therewith randomly occurringsubpulses having risetimes less than said predetermined risetime value,and at least a selected one of said electrical signals having a signalstrength in excess of a predetermined threshold value; detectingrisetimes of at least a selected one of said electrical signals receivedby said receiving means less than said predetermined risetime value anddetecting at least a selected one of said electrical signals with asignal strength greater than said predetermined threshold value; formingand transmittimitting an integration control signal of a predeterminedintegration interval when risetimes less than said predeterminedrisetime value and signal strengths greater than said predeterminedthreshold value are detected substantially simultaneously; transmittinga peak detect signal during said integration informal interval whenevera risetime less than said predetermined risetime value is detected;integrating said E and H field components separately for the duration ofsaid first control signal; sampling the said electrical signalsassociated with said E_(V) E and H₁ and H₂ field components fields inresponse to said peak detect signals; forming an absolute sum of saidelectrical signal strengths associated with said H₁ and H₂ fields andgenerating an electrical signal associated therewith; integrating saidelectrical signal associated with said E field and said electricalsignal associated with said absolute sum; converting said integrated andsampled E and H field components electrical signals to digital signalsrepresenting the signal strengths of said integrated and sampledelectrical signals; transmitting said digital signals to a programmablemicroprocessor in response to microprocessor control signals wherebysaid microprocessor determines the direction of and distance to saidlightning strokes; and displaying the location of said lightning strokesin response to the determination of said microprocessor of saiddirection and distance.
 18. An apparatus for determining the location oflightning strokes, each lightning stroke generating electric (E) andmagnetic (H) field components, said apparatus comprising:receiving meansfor receiving separately the electric (E) and magnetic (H) fieldcomponents of a lightning stroke and for generating electrical signalsassociated with said E and H field components, said electrical signalscharacterized by an initial rise time and a plurality of subsequent subpulse risetimes; and means coupled to said receiving means fordetermining the distance to said lightning stroke from said apparatus inresponse to said electrical signals associated with both said E and Hfield components, by operating upon said electrical signals associatedwith both said E and H field components, and for determining thedirection to said lightning stroke relative to said apparatus inresponse to said sub pulses of said electrical signals associated withboth said E and H field components.
 19. The means coupled to saidreceiving means as claimed in claim 18 comprising:sampling circuit meansfor sampling said electrical signals in response to said subpulseswhereby sample signals of said electrical signals are generated.
 20. Themeans coupled to said receiving means as claimed in claim 19comprising:processing means coupled to said sampling means fordetermining the direction to said lightning stroke relative to saidapparatus in response to said sample signals.
 21. The processing meansas claimed in claim 19 for determining the distance to said lightningstroke from said apparatus in response to said sample signals.
 22. Themeans coupled to said receiving means as claimed in claim 18comprising:integration circuit means for integrating separately over apredetermined time interval said electrical signals associated with saidE and H field components, whereby integrated electrical signals aregenerated; and processing means coupled to said integration circuitmeans for determining the distance to said lightning stroke from saidapparatus in response to said integrated electrical signals.
 23. Theprocessing means as claimed in claim 22 wherein said processing meansdetermines the distance to said lightning stroke from said apparatus bycomparing a ratio of said integrated electrical signals to predeterminedvalues representative of distance.
 24. The means coupled to saidreceiving means as claimed in claim 18 comprising:integration circuitmeans for integrating separately over a predetermined time interval saidelectrical signals associated with said E and H field components,whereby integrated electrical signals are generated; and processingmeans coupled to said integration circuit means for determining thedirection to said lightning stroke relative to said apparatus inresponse to said integrated electrical signals.
 25. The processing meansas claimed in claim 24 wherein said processing means determines thedirection to said lightning stroke relative to said apparatus bycomparing said integrated electrical signals with each other todetermine an angle representative of direction.